Nervous system disorders affect millions of people, causing a degradation of life, and in some cases, death. Nervous system disorders include disorders of the central nervous system, peripheral nervous system, and mental health and psychiatric disorders. Such disorders include, for example without limitation, epilepsy, Parkinson's disease, essential tremor, dystonia, and multiple sclerosis (MS). Additionally, nervous system disorders include mental health disorders and psychiatric disorders which also affect millions of individuals and include, but are not limited to, anxiety (such as general anxiety disorder, panic disorder, phobias, post traumatic stress disorder (PTSD), and obsessive compulsive disorder (OCD)), mood disorders (such as major depression, bipolar depression, and dysthymic disorder), sleep disorders (e.g., narcolepsy), obesity, and anorexia.
As an example, epilepsy is a serious neurological disease prevalent across all ages. Epilepsy is a group of neurological conditions in which a person has or is predisposed to recurrent seizures. A seizure is a clinical manifestation resulting from excessive, hypersynchronous, abnormal electrical or neuronal activity in the brain. A seizure is a type of adverse neurological event that may be indicative of a nervous system disorder. This electrical excitability of the brain may be likened to an intermittent electrical overload that manifests with sudden, recurrent, and transient changes of mental function, sensations, perceptions, and/or involuntary body movement. Because the seizures are unpredictable, epilepsy affects a person's employability, psychosocial life, and ability to operate vehicles or power equipment. It is a disorder that occurs in all age groups, socioeconomic classes, cultures, and countries. In developed countries, the age-adjusted incidence of recurrent unprovoked seizures ranges from 24/100,000 to 53/100,000 person-years and may be even higher in developing countries. In developed countries, age-specific incidence is highest during the first few months of life and again after age 70. The age-adjusted prevalence of epilepsy is 5 to 8 per 1,000 (0.5% to 0.8%) in countries where statistics are available. In the United States alone, epilepsy and seizures affect 2.3 million Americans, with approximately 181,000 new cases occurring each year. It is estimated that 10% of Americans will experience a seizure in their lifetimes, and 3% will develop epilepsy by age 75.
There are various approaches in treating nervous system disorders. Treatment therapies can include any number of possible modalities alone or in combination including, for example, electrical stimulation, magnetic stimulation, and/or drug infusion. Each of these treatment modalities can be operated using closed-loop feedback control. Such closed-loop feedback control techniques receive neurological signals (e.g., from a monitoring element) carrying information about a symptom or a condition or a nervous system disorder. Such a neurological signal can include, for example, electrical signals (such as electroencephalogram (EEG), electrocorticogram (ECoG), and/or electrocardiogram (EKG) signals), chemical signals, other biological signals (such as changes in the quantity of neurotransmitters), temperature signals, pressure signals (such as blood pressure, intracranial pressure or cardiac pressure), respiration signals, heart rate signals, pH-level signals, and peripheral nerve signals (such as cuff electrodes placed on a peripheral nerve). Monitoring elements can include, for example, recording electrodes or various types of sensors.
For example, U.S. Pat. No. 5,995,868 to Dorfineister et al., incorporated herein by reference in relevant part, discloses a system for the prediction, rapid detection, warning, prevention, or control of changes in activity states in the brain of a patient. Use of such a closed-loop feed back system for treatment of a nervous system disorder may provide significant advantages. For example, it may be possible for treatment to be delivered before the onset of the symptoms of the nervous system disorder.
In the management of a nervous system disorder, it may be important to determine an extent of a neurological event, a location of the neurological event, a severity of the neurological event, and the occurrence of multiple neurological events in order to prescribe and/or provide a delivery of a treatment or otherwise manage the neurological disorder. A patient, for example, would not benefit from a medical device system if the patient experienced a neurological event but was not administered treatment because the medical device system did not detect the neurological event. On the other hand, a patient may suffer adverse effects, for example, if subjected to a degree of treatment corresponding to multiple neurological events, such as seizures, when in fact the patient had experienced only one neurological event, or a series of minor events, or no neurological event at all. As used herein, the term “neurological event” may encompass physiological events, such as seizures, as well as events defined artificially, for example, by measurable signal processing parameters.